🚀 go-pugleaf

Once more, with feeling.

Lots of (most?) automatic failure notices aren't sent to any address
taken from the mail header, but are sent to the envelope-from
information.  This envelope-from information is transmitted in SMTP in
the ``MAIL FROM:'' command, is recorded at final delivery time in old
Unix mail in the From_ (``From '') header, and is recorded at final
delivery time in Internet-style mail in the Return-path: header.

RFC 822, describing only headers, suggests that automatic error messages
be sent to the content of the Sender: field of the message header.  Lots
of (most?) mailers use the RFC 821 option of sending error messages to
the envelope-from address information instead.

Sendmail gets the envelope-from information from its -r and -f options. 
However, you can get (some versions of) it to override this information
if you use its alias expansion to do the redistribution.  I believe that
if you have, say, ``foo-list'' set up as your exploder address, sendmail
also looks for an ``owner-foo-list'' alias, and if it finds it, uses its
content to replace the envelope-from address information.

Free advice: don't muck with the headers of redistributed mail; leave
``From:'' and ``Reply-to:'' alone.  Change the envelope-to (and
envelope-from) information without changing the headers.

		Craig Everhart